Digital broadcast systems typically transmit one or more high-bandwidth signals, each of which is typically composed of a stream of data or data packets having a plurality of video, audio and/or other digital programs or content multiplexed therein. A number of well-known data compression techniques (e.g., audio/video content compression techniques), transmission protocols and the like are typically employed to generate and transmit a multi-program data stream or bit stream, which is commonly referred to as a transport stream. In particular, digital television programming is typically transmitted according to a standard promulgated by the Advanced Television Standards Committee (ATSC). The ATSC standard is a comprehensive standard relating to the conveyance of digital television signals. Under the ATSC standard, video information associated with a program is encoded and compressed according to the well-known Moving Pictures Expert Group-2 (MPEG-2) standard and audio information associated with the program is encoded and compressed according to the well-known AC-3 standard. As a result, an ATSC data stream or bit stream contains video information in the form of MPEG-2 packets and audio information in the form of AC-3 packets. However, other digital transmission protocols, data compression schemes and the like may be used instead.
Some digital broadcasters enable the identification of digital broadcast programs (e.g., at home sites, reference sites, etc.) by inserting or embedding digital program identification information and/or other data (e.g., watermark data) in the video and/or audio bit stream. The inserted or embedded digital data is commonly referred to as audience measurement data or content identification data, which may include signal identification codes (i.e., digital codes that are uniquely associated with respective audio/video content portions or programs), date information, time information, consumer identification information, etc. The insertion of audience measurement data at the distribution system headend or broadcast station is commonly referred to as an active audio/video content identification process because the system headend or broadcast station actively modifies (i.e., inserts or embeds data in) the transmitted bit streams or transport streams.
Typically, known active data insertion or embedding techniques insert or embed digital data within each of the video and/or audio signals that make up the one or more programs (i.e., video and/or audio programs) being transmitted by the broadcast station before the individual video and/or audio signals are compressed and multiplexed to form a single multi-program bit stream or transport stream. However, because the digital data are inserted in an uncompressed domain (i.e., within the individual uncompressed audio/video signals), multiple digital data insertion or embedding devices (e.g., one for each uncompressed program bit stream) are typically required. This requirement for multiple digital information insertion devices is undesirable because it increases the complexity and operational costs associated with headend or broadcast stations.
Another difficulty that results from inserting or embedding digital data into individual uncompressed program signals is that subsequent compression operations (e.g., compression encoding) may corrupt and/or eliminate some or all of the inserted or embedded data. As is known, signal compression techniques usually provide a substantial reduction in the quantity of data needed to reproduce a video image and/or an audio signal, but do so at the expense (i.e., the loss) of at least some data or information. Thus, if compression operations corrupt the inserted digital data, the home site and/or a central data processing or collection facility may not be able to accurately identify audio/video content.
As noted above, the digital data inserted or embedded by existing broadcast systems may include watermark data or information, which is typically inserted or embedded in audio and/or video content data stream. However, many existing watermarking techniques are designed for use with analog broadcast systems. In particular, existing watermarking techniques typically convert analog program data to an uncompressed digital data stream, insert watermark data in the uncompressed digital data stream, and convert the watermarked data stream back into an analog format prior to transmission. Thus, when used with digital audio and/or video systems, existing watermarking techniques may decompress the compressed digital data stream into time-domain samples, insert the watermark data into the time-domain samples, and recompress the watermarked time-domain samples into a watermarked compressed digital data stream. However, such decompression/compression cycles may cause degradation in quality of the original audio and/or video content.